1. Field of the Invention
The present invention relates to an automatic shifting-operation control system which automatically controls a transmission of a vehicle in accordance with a driving state detected during a driving of a vehicle. More particularly, the invention relates to an automatic shifting-operation control system capable of automatically controlling a transmission of a vehicle in the like manner as normal driving state even when the vehicle drives with a reduced amount of fuel injection by means of a vehicle speed limiting function or even during automatic cruising by employing a cruise function.
2. Description of the Related Art
Conventionally, a shifting point of transmission control of an automatic or a semi-automatic shifting-operation control system is determined by a map of shifting based on an accelerator opening amount and an engine rotating number. This is because that the accelerator opening amount is suited for detecting driver's intension of acceleration and deceleration during vehicle driving, and that a load applied to the vehicle can be estimated by checking both the steady accelerator opening amount state and the engine rotating number. Such a technique is described on page 30 of the publication entitled “State-of-Art technologies of power transmissions in '98” distributed in No. 9806 JSAE SYMPOSIUM held on Nov. 13, 1998 by the Society of Automotive Engineers of Japan.
To meet the speedup of vehicles accompanied by, for example, development of expressways, the output of a vehicle's engine has been increased and the number of stages of gear of a transmission has been increased. On the other hand, it is also required to reduce the driving cost by improving consumption of fuel. Hence, to improve the fuel consumption, it might be conceived to suppress the maximum engine rotating number. For example, to suppress the vehicle speed to a predetermined limited value, there is a technique in which a normal fuel supply amount obtained from the accelerator opening amount and the engine rotating number, and fuel supply amount determined by the vehicle speed to limit a vehicle speed are compared with each other, and smaller one of the fuel supply amount is chosen, so that the fuel supply amount to the engine is reduced so as to limit the maximum engine rotating number. This technique is described in, for example, Japanese Unexamined (Kokai) Patent Publication No. 10-252520.
Nevertheless, in a vehicle having such a conventional automatic or semi-automatic shifting-operation control system and engine control means including a vehicle speed limiting function which reduces the fuel injection amount for suppressing the driving speed of the vehicle to less than or equal to the predetermined control value, during the operation of the vehicle speed limiting function of the engine control means, the fuel injection amount is limited by the control operation done by the engine side. Thus, a desired engine rotating condition in compliance with a depression amount of the accelerator pedal by a driver cannot be acquired. For this reason, when the vehicle is accelerated with a lower gear stage, the engine rotating number does not reach a predetermined up-shifting engine rotating number in accordance with the accelerator opening amount, and if the driver continues depressing of the accelerator pedal, the gear is reluctantly held at an intermediate gear stage and cannot be sufficiently shifted up in some cases. Further, the vehicle is not accelerated although the accelerator pedal is depressed, and this state might be erroneously identified as being at a high load state such as during hill climbing.
From the reasons described above, it becomes necessary to newly incorporate an automatic shift determination controller which can work to estimate a load based on the fuel injection amount and the engine rotating number that can be indication of substitutive characteristics and in addition, to produce a shifting map based on such a conception that is quite different from the conventional shifting map. Thus, past experience can not be used for extracting therefrom parameters usable for adjusting a driving performance of a vehicle and accordingly, efficiency in the controlling operation is often deteriorated.
In a vehicle having the conventional automatic or semi-automatic shifting-operation control system and engine control means having a cruise control function capable of achieving an automatic cruise by setting a driving speed of the vehicle to an optional constant speed, during cruising-controlling operation for the automatic cruise is being carried out, the vehicle drives in a state such that a driver releases his or her foot from the accelerator pedal, the load of the vehicle cannot be estimated from the accelerator opening amount. From these reasons, it becomes necessary to newly incorporate an automatic shifting-operation determination controller which estimates a load from the fuel injection amount and the engine rotating number that can be indication of substitutive characteristics, and to produce a shifting map based on such a conception that is quite different from the conventional shifting map. Thus, for example, past experience cannot be used for extracting therefrom parameters usable for adjusting a driving performance of a vehicle and accordingly, efficiency in the controlling operation is often deteriorated.